$StartDirectory = "C:\Projects\May 2012 Silverlight Toolkit\Source"
$FileFilter = "*.csproj"

$children = Get-ChildItem $StartDirectory -Filter $FileFilter -Recurse | select FullName

Foreach($child in $children)
{
  
   $a = Get-Content $child.FullName 
   $Summation = @()
   Foreach ($b in $a)
   {
      $c= $b.Replace('Microsoft.Windows.Design.Interaction, Version=4.0.0.0, Culture=neutral', 'Microsoft.Windows.Design.Interaction, Version=4.1.0.0, Culture=neutral')  #| Get-Member
	  $Summation += $c.Replace('Microsoft.Windows.Design.Extensibility, Version=4.0.0.0, Culture=neutral', 'Microsoft.Windows.Design.Extensibility, Version=4.1.0.0, Culture=neutral')  #| Get-Member
   }
   Set-Content -path $child.FullName -value $Summation
}

 # (Get-Content $child.FullName) |
  # % { $_ -replace ('Microsoft.Windows.Design.Interaction, Version=4.0.0.0, Culture=neutral', 'Microsoft.Windows.Design.Interaction, Version=4.1.0.0, Culture=neutral')
                    # replace ('Microsoft.Windows.Design.Extensibility, Version=4.0.0.0, Culture=neutral', 'Microsoft.Windows.Design.Extensibility, Version=4.1.0.0, Culture=neutral')
	#				} |
   #Set-Content $child.FullName